Preparation of mixed cellulose esters containing a substantial amount of propionyl or butyryl



Patented July 23, 1940 PREPARATION OF aztasae PATENT, OFFICE MIXED CELLULOSE ESTEBS CONTAINING A SUBSTANTIAL AMOUNT OF PROPIONYL R BUTYRYL Loring W. Blanchard, Jn, Rochester, N. Y.,

asslgnor to Rochester, N. Y., a

Eastman Kodak Company,

a corporation of New No Drawing. Application December 18, 1937,

Serial No. 180,602

butyrate with an estei-iflcationbath, at least 60% a of the total acyl content of which consists of propionyl and/or butyryl, in which hath not more than five parts of fatty acid are present, for each part of cellulose, and the ester so prepared.

In the preparation of cellulose acetate-propionate or cellulose acetate-butyrate, with an esteriflcation bath containing at least 60% of propionyl or butyryl based on the total acyl, many diiflcultiesare involved due to the sluggishness of the reaction mixture. As a consequence, the viscosity of the cellulose is detrimentally lowered before sufllcient esterification has occurred to protect it from the degrading influences present in the reaction mixture. If the various known means of speeding up the reaction,

such as the use of heat or increasing the amount so of catalyst, are applied, the degrading tendency of the reaction mixture is increased and, although the time of reaction. is shortened, the rate of lowering of the viscosity is accelerated. Various methods have been proposed for making cellulose acetate-propionates and cellulose acetate-butyrates but, in every case, either a high acetyl ester was prepared. or the amount of diluent present was so great that the viscosity of the ester wasexcessively lowered. Also, in some cases of preparing high propionyl or high butyryl esters, the cellulose has been pretreated with glacial acetic acid containing a catalyst. These processes all result in the preparation of cellulose esters in which the viscosity is excessively a lowered. I

One object of my invention is to prepare mixed esters of cellulose having a high contentof propionyl or butyryl. Another object of my invention is to provide a method of preparing 0 those esters in which the cellulose is not excessively broken down. A further object of 'my invention is to provide mixed esters having a high content of propionyl or butyryl, which esters,

55 esterifying bath, and 343% (based on the cellu-.

lose) of sulfuric acid catalyst, a product of higher viscosity is obtained than would be obtained in any of the processes of the prior art. I have found that, by decreasing the amount of fatty acid, which is the only solvent present in the esteriflcation bath, the concentration ofthe anhydride is increased so that, even though propionic or butyric anhydride is employed therein, the reaction is speeded up and approaches that which would be obtained if acetic anhydride were used. This more rapid esterification adds suflicient acyl groups to the cellulose, in the early stages of; the esteriiication, to protect it from excessive viscosity reduction by the sulfuric acidor other catalyst which may be'present.

- and, thus, the final product has a good viscosity.

Also, my process results in the use of a shorter reaction time and thereby increases the yield possible per acylaticn vessel. The esters prepared by my process are markedly free from fiber having a high clarity.

The cellulose acetate-propionates and cellulose acetate-butyrates, obtained by my process, have v'iscosities from 200 cps. to 4000 cps. in a 10% solution in acetone at 25 C., Sheeting may be prepared from these esters ,by dissolving them in acetone, ethylene chloride or propylene chloride, or their mixtures with a small amount of alcohol, if soluble therein, and coating them out onto a film forming surface. These esters may also be employed for laminating with glass, metal, wood or other material, preferably in sheet form. Due to the clarity of the solution of these esters, the sheeting prepared therefrom is especially desirable in the making of laminated glass or photographic lilm, in whicha high degree of clarity is very desirable.

In processes in accordance with my invention, the maximum temperature should be between 70 and 110 F., and preferably between 80 and 100 F. For the higher viscosity esters, the maximum temperature reached in the reaction should not exceed 80 F. and, in the preparation of the medium viscosity esters, a maximum temperature of 100F. would be sufilcient in most cases.

The amount of sulfuric acid-employed is preferably kept as low as possible to obtain a good acetylation at the temperature employed. For the preparation of the higher viscosity esters, in which a. low maximum temperature is'employed, 5-6% of the sulfuric acid is usually sufiicient.

- For the medium viscosity esters, in which a higher maximum temperature is permissible, 3-5% of sulfuric acid is usually suflicient. If

20 and grain and, therefore, are good quality esters desired, phosphoric acid may supplement the sulfuric acid which is employed. V

In the preparation of the medium viscosity esters, the use of not more than 3-4% of sul 5 furic acid is preferred. With higher percentages of sulfuric acid, in the preparation of the medium viscosity esters, a tendency towards introducing more sulfur into the product and lowering of its heat stability is present. Also, in using the higher temperature, such as 110 F., the viscosity of the product will usually be lower with the use of a higher percentage of sulfuric acid catalyst. It is to be understood that the percentages of sulfuric acid in this specification are based on "the weight of the cellulose.

It is preferable that at least three parts of fatty acid be present in the esterification bath for each partof cellulose, although this lower limit is governed by the type of ester being prepared and the amount of excess anhydride present. If a medium viscosity ester .is being prepared, it is not necessary that as much solvent be present to dissolve it as with the higher viscosity esters and, therefore, in some cases, as low as two .5 parts of fatty acid might be employed for each part of cellulose. Obviously, if a large excess of anhydride is employed, the proportion of fatty.

acid present need not be so great to obtain solution. It is of advantage that not more than a I) slight excess of anhydride over that required to Y react with the cellulose be employed as, in this way, the generation of heat when the excess anhydride is destroyed'by the addition of water or dilute acid, after the reaction has occurred, is &' maintained at a minimum and, thus, any danger of seriously lowering the viscosity at this point is avoided.

If some other solvent diluent is used, the proportion of fatty acid should be restricted so that 40? the total amount of diluent employed is not more -than five parts to one part of cellulose. Some solvent'diluents which have been suggested for use in esterification processes are: ethylene chloride, methylene chloride, chloracetic acid and 6 metiroxy-acetic acid.

The propionyl and/or butyryl content in the esterification bath should be at least 60%, based on the total acyl. Ifa proportion in the neighborhood of 60% of. acyl .groups of 3-4 carbon 50 atoms (based on total acyl) is used in the esterification bath, the resulting ester will contain approximately propionyl and/or butyryl, basedon the total ester, or approximately 40% based on the total acyl content. If approximately 90% ll of propionyl and/or butyryl, based on the total acyl in the bath, is employed, the proportion of propionyl and/or butyryl in the final product,

based on the. total acyl, will be approximately' 80%. The product, made in accordance with my Q invention, will be of good clarity, showing the absence of poorly acylated or unacylated fibers and .willhaveaviscosityofatleastzoocentipoisesin a 10% solution in acetone at (2., showing the absence of an excessive lowering of viscosity in the esterlfication.

Due to the increased effectiveness of the propionic or butyric anhydride employed in the esterification of the cellulose, not only is. an esterof good viscosity-and high clarity obtained, but

- 79 the time of the esterification is speeded up by at least one-third. and usually more, over the time required in a similar esteriflcation using a greater amoimt of solvent. v

Because of the avoidance of an excessive lowll erlng of viscosity, my process is particularly adapted to prepare cellulose esters of high viscosity, such as 2,000 to 4,000 centipoises. These high viscosity esters may be obtained, by my process, from cellulose having the same ouprammonium viscosity as that of the cellulose ordi- .5 narily employed as the starting material in the making of cellulose organic esters. Although cotton linters are preferred for the starting material, other esterifiable cellulosic materials may be employed. For instance, refined wood pulp, such as 10 high alpha sulfite pulp, may be used advantageously. It will be found that, regardless of the cellulose used, the viscosity of the resulting product will be high, compared with a similar process in which the proportion of solvent is not limited. 15 To obtain cellulose esters of good viscosity, it is desirable that an undegraded cellulose materialbe employed. For this reason, it isdesirable that the pretreatment bath be substantially free of catalyst, particularly sulfuric acid, so that the 20 viscosity of the cellulose will not have been adversely affected prior to its esterification.

The following examples illustrate processes embodying my invention:

. Example I pounds of refined cotton linters were treated with 60 pounds of glacial aceticacid for four hours at 120-F. 105 pounds of 98% propionic anhydride and 55 pounds of propionic acid were 30 added as the mass was cooled to 50 F. A solution of 448 cc. of sulfuric acid in 20 pounds of propionic acid was then added. The temperature was allowed to rise to 70 F. and kept at '70-80 1?. Nine hours after the addition of the sulfuric acid catalyst, the reaction was finished. A batch of excellent appearance was obtained. A mixture of 36 pounds of water and 72 pounds of acetic acid was then added and the cellulose ester was hydrolyzed by maintaining the mass at 100 F. 40 for 36 hours. The ester was then precipitated, washed and dried. It exhibited a viscosity of 2470 centipoises in a 10% solution in acetone at 25 C.

. Example I! Three pounds of refined cotton linters were treated with three pounds of glacial acetic acid for four hours at 110 F. A mixture of 9.2 pounds of butyric acid, 4.8 pounds of butyric anhydride (95%) and five pounds of acetic anhydride (95%) was added as the mixer, containing the mass, was cooled to 50 F. A solution of 44.8 cc. of sulfuric acid in two pounds of butyric acid was added.

The temperature was allowed to rise to 80 F. and

in accordance with this example had a viscosity oi-3,200 centipoises in a 10% solution of acetone at 25 C.

Thepretreatment of thecellulose becarried out in accordance with that described and claimed in Malm application Serial No. 81.323.-

filed May 22, 1936, by putting the cenmose in sheet i'orm'and passing it over a roll moistened with acetic acidor with a pretreatment mixture within the limits described above and allowing it to stand'until the cellulose is sufliciently activated. In the pretreatment, it is necessary that the pretreatment liquid be well distributed through the cellulose material, so that the treatment is uniform. It is also necessary that the pretreatment bath be catalyst-free, so as to swell the cellulose without adversely afiecting its viscosity.

It is preferred that the pretreatment bath be concentrated acid, that is, contain at least 90% of acid. The use of more dilute acid, if aqueous, is not e'conomical, due to the tendency of the water to destroy anhydride in the esterification. If, however, the diluent is inert, this disadvantage is not present.

As my process makes possible the esterification of cellulose in a bath containing a high, percentage of propionyl or butyryl, without breaking down the cellulose, it is particularly directed to I making cellulose esters having high or moderately high viscosities, together with high propionyl and/or butyryl contents. The esters made in accordance with my invention are of value, either hydrolyzed or unhydrolyzed, for the making of sheeting or film by coating out a solution of the same in acetone, or an alkylene chloride, such as ethylene chloride on a film-forming surface. The

sheeting thus prepared may be employed in the 2 making of photographic film, laminated glass or for any purpose where a clear, flexible, moistureresistant sheet finds use.

The esters made in accordance with my invention may be employed in any connection wherein an ester of .the viscosities obtained is suitable for moisture and areamenable to the solvent action of a large number of solvents.

I claim:

1. -A process of preparing cellulose actate-propionate, which comprisestreating 100 parts of cotton linters with 200 parts of glacial acetic acid for four hours at approximately 170 F., then adding a mixture of 350 parts of propionic anhydride and 185 parts of propionic acid as the mass is cooled to approximately F. and, then, adding a solution of six parts of sulfuric acid in 67 parts of propionic acid, allowing the temperature to rise to 70 F. and maintaining it between ing 100 parts of cellulose with200 parts of glacial 70-80 F. until the reaction is completed.

2. A process of preparing a high viscosity mixed ester of cellulose which comprises treat:

acetic acid for four hours at approximately 170 F., adding a mixture of 185 parts of a fatty acid of 3-4 carbon atoms and 350 parts of an anhydride of such an acid, as the mass is cooled to approximately 50 F. and then adding a solution of 6 parts of sulfuric acid in 67 parts of a fatty acid of 3-4 carbon atoms, allowing the temperature to rise to 70 F. and maintaining it between 70-80 F. .until the reaction is completed.

3. A process .of preparing a high viscosity mixed ester of cellulose having a propionyl and butyryl content of at least 20% which comprises activating the celllulose with a catalyst-free fatty adding a solution of 3-8% of sulfuric acid (based maintaining it at on the 'weightof the cellulose) in fatty acid of 34 carbon atoms, the amount of fatty acid sup-,

plied by the pretreatment and the subseque t ad- These esters exhibit good resistance to ditions being such that the esterification bath is a solvent for the cellulose ester to be form 2d,

contains at least three and not more than five parts of fatty acid to one of cellulose so that at least of the total acyl of the bath is propionyl and butyryl and allowing the temperature to rise to a maximum of -110 F., the maximum being selected inversely to the percentage thereto as the mass is cooled to approximately 50 F., the anhydride being an an amount slightly in excess oftheoretical, and then inducing esterification by adding a solution of 3-8% of sulfuricacid (based on the weight of the cel lulose) in butyric acid, the amount of fatty acid supplied by the pretreatment and the subsequent additions being such that the esterification bath is a solvent for the cellulose ester to be formed,

contains at least three and not more than five.

parts of fatty acid to one of cellulose and so thatat least-60% of the total acyl of the bath'is butyryl and allowing the temperature to rise to a maximum of '70-1l0 F., the maximum being selected inversely to the percentage of catalyst. 5. A process of preparing a high viscosity mixed ester of cellulose having a propionyl and butyryl content of at least 20% which comprises activating the cellulose with a catalyst-free fatty acid bath containing at least 40% of acetic acid,

adding a mixture of fatty acid of 3-4 carbon.

atoms and the anhydride of such acid, as the mass is cooled to approximately 50 F., the anhydride being slightly in excess of theoretical, and then inducing esterification by adding asolution of 5-6% of sulfuric acid (based on the weight of the cellulose) in fatty acid of 3-4 carbon atoms,

the amount of fatty acid supplied .by the pretreatment and .the subsequent additipns being such that the esterification bath is a solvent for the cellulose ester to be'formed, contains at least three and not more than five parts of fatty acid to one of cellulose and so that at least 60% of the total acyl of the .bath is propionyl and butyryl and allowing the temperature to rise to 70 F. and'maintaining it at 70-80" F. until the reaction is completed..

6 A processof preparing a high viscosity acetate butyrate of cellulose having a butyryl content of at least 20% which comprises activating the cellulose with a catalyst-free fatty acid bath containing at least 40% of acetic acid, adding a mixture -of butyric acid and the anhydride of such' acid, as the mass is cooledto approximately 50 F., the anhydride being slightly in .excess of theoretical, and then inducing esterification by adding a solution of 5'-6% of sulfuric acid (based on the weight of the cellulose) in butyric acid, the amount of fatty acid supplied by the pretreatment and the subsequent addi'-' tions being such that the esterification bath is a solvent for the cellulose ester to be formed, contains at least three and not more than five parts of fatty acid to one of cellulose and so that at least 60% of the total acyl of the bath is butyryl, allowing the'temperature to-rise to 70 F. and IO- F. until the reaction is completed.

LORING W. BLANCHARD, JR. 

